This invention relates to a lock of the type intended to be operated by a web-type key, comprising a plate with latches which is actuated by said key and having a consent stud, and a set of tumbler actuated by the same key and each having a window with teeth, said window being traversed by said consent stud of the plate with latches, in order to allow the displacement of the stud and the latches only by action of a key whose web is provided with a predetermined sequence of projections and recesses.
In the known constructions, said consent stud of the plate with latches has the shape of a prism with a constant cross-section, and the teeth of the windows of the various tumblers have each a length determined as a function of the radius, relative to the axis of rotation of the key, of the corresponding projection or recess of the web, the recesses being defined by and between the projections, whereby, under the action of the key, the free spaces between the teeth of the windows of all tumblers come into alignment to allow the consent stud of the plate with latches to pass between them. In the locks with a key having two opposite non-symmetrical webs, the teeth of even position of each tumbler are not equal to the teeth of odd position of the same tumbler lever, because this provision makes more difficult the unauthorized opening of the lock. However, these constructions have some disadvantages.
A first disadvantage of the known locks of the type being considered consists in the high construction and assembly costs, due to the fact that a lot of tumblers are to be provided, each of them corresponding, as regards the length of the teeth of its windows, to a specific pair of measures of the projections and the opposite recesses of the key, and once the key intended to actuate a specific lock has been manufactured, the lock must be assembled by choosing, in the correct sequence, the different tumblers corresponding to the successive pairs of projections and recesses of the key. The manufacture of the different tumblers requires use of a lot of different dies or of an expensive die with slides to be set exactly into various pre-established positions, and the assembly of the lock requires the attentive intervention of skilled operators.
Another disadvantage of the locks in question consists in that it is not possible to modify at a later time a lock constructed for being actuated by a certain key, so as to make it operable by a different key, as would be desirable whenever the original key had to be entrusted to a person who can perhaps have provided a duplicate thereof, a case which routinely occurs when installing the lock, if this latter is not personally installed by the user, and is often repeated on the occasion of work being carried out on the premises protected by the lock and on other occasions. Such a modification is possible, even if at the cost of a relatively difficult operation and the replacement of a complex component, in some types of cylinder locks, which on the other hand have a safety degree which is smaller than that of the tumbler locks.